Should be a fairly obviously choice for you.
If you watch a lot of movies or TV, then the TV. If you play (or want to play) a lot of new games, then the computer. If it's an HDTV then there's not much point picking one up if you don't already have or aren't planning to get a HD player of some kind.
If you play, or want to play, new games and your current PC is more than a couple of years old, then get the PC. But there's no point getting a split new PC if the only thing you do is surf the net or play really old games.
If you do none of that, then save the money. If you do both, then flip a coin.
Dagnammit